1. Field of the Invention
The present invention is directed to a permanent magnet of the type SE-Fexe2x80x94B that has the tetragonal phase SE2Fe14B as the principal phase, wherein SE is at least one rare earth element, including Y.
2. Description of the Prior Art
A magnet of the above general type is disclosed, for example, in European Application 0 124 655 and in U.S. Pat. No. 5,230,751 that corresponds therewith. Magnets of the type SE-Fexe2x80x94B exhibit the highest energy densities currently available. SE-Fexe2x80x94B magnets manufactured by powder metallurgy contain approximately 90% of the hard-magnetic principal phase SE2Fe14B.
German OS 41 35 403 discloses a two-phase magnet, wherein the second phase can be a SE-Fexe2x80x94Coxe2x80x94Ga phase.
European Application 0 583 041 likewise discloses a two-phase magnet, whereby the second phase is composed of a SE-Ga phase.
U.S. Pat. No. 5,447,578 discloses a SE-transition metal-Ga phase.
One usually proceeds such in the manufacture of such SE-Fexe2x80x94B magnets by combining a SE-Fexe2x80x94B base alloy with a composition close to the SE2Fe14B phase and a binder alloy with a lower melting temperature. The goal is to set the structure of the SE-Fexe2x80x94B sintered magnets of SE2Fe14B base alloys with inter-granular binders, while using optimally little binder alloy.
European Application 0 517 179 proposes the employment of binder alloys having the composition Pr20Dy10Co40B6Ga4Ferest (in weight percent, this is Pr≈35, Dy≈20, Co≈28, B≈0.77, Ga≈3.5).
It has now turned out that the proportion of this binder alloy in the mixture of the base alloy must lie within 7-10 weight %. In this mixing range, sinter densities of approximately xcfx81 greater than 7.55 g/cm3 are achieved only at sintering temperatures above 1090xc2x0 C. These sinter densities roughly correspond to 99% of the theoretical density. Outside this mixing range, the sinterability and, thus, the remanence that can be achieved are considerably influenced. The grain growth is highly activated in the magnets with a proportion of this binder alloy of more than 10 weight %, but the pores are not closed. The consequence is the formation of a structure with anomalously large grains ( greater than 50 xcexcm) and with high porosity as well as with low sinter densities. Given lower proportions of binder alloy, the amount of the fluid phase is accordingly not adequate for the densification.
It is an object of the present invention to provide a powder-metallurgical manufacturing method for permanent magnets of the SE-Fexe2x80x94B type that exhibits an enhanced sinterability upon reduction of the proportion of binder alloy compared to the known methods and also achieves a very good remanence.
The object is inventively achieved by a method that comprises the following steps:
a1) a powder of a base alloy of the general formula
SE2T14B, 
wherein SE is at least one rare earth element, including Y, and T is Fe or a combination of Fe and Co, whereby the Co part does not exceed 40 weight % of the combination of Fe and Co,
a2) and powders of at least two binder alloys of the general formulas
SE6(Fe, Co)13xe2x88x92xGa1+x 
and
xe2x80x83SE2CO3 
wherein SE is at least one rare earth element, including Y, and wherein 0xe2x89xa6xxe2x89xa62, are mixed in a weight ratio of 99:1 to 89:11;
b) the mixture is compressed and, subsequently,
c) is sintered in a vacuum and/or in an inert gas atmosphere.
It has been shown that permanent magnets manufactured in this way exhibit very high remanences, and that the proportion of binder alloy compared to the proportion of the base alloy can be reduced to below 7 weight %. Further, the additional gallium-containing phase of the binder alloy exhibits especially good wetting properties.